'\" et
.TH GMTIME "3P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\"
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
.\"
.SH NAME
gmtime,
gmtime_r
\(em convert a time value to a broken-down UTC time
.SH SYNOPSIS
.LP
.nf
#include <time.h>
.P
struct tm *gmtime(const time_t *\fItimer\fP);
struct tm *gmtime_r(const time_t *restrict \fItimer\fP,
    struct tm *restrict \fIresult\fP);
.fi
.SH DESCRIPTION
For
\fIgmtime\fR():
The functionality described on this reference page is aligned with the
ISO\ C standard. Any conflict between the requirements described here and the
ISO\ C standard is unintentional. This volume of POSIX.1\(hy2017 defers to the ISO\ C standard.
.P
The
\fIgmtime\fR()
function shall convert the time in seconds since the Epoch pointed to by
.IR timer
into a broken-down time, expressed as Coordinated Universal Time
(UTC).
.P
The relationship between a time in seconds since the Epoch used as an
argument to
\fIgmtime\fR()
and the
.BR tm
structure (defined in the
.IR <time.h> 
header) is that the result shall be as specified in the expression
given in the definition of seconds since the Epoch (see the Base Definitions volume of POSIX.1\(hy2017,
.IR "Section 4.16" ", " "Seconds Since the Epoch"),
where the names in the structure and in the expression correspond.
.P
The same relationship shall apply for
\fIgmtime_r\fR().
.P
The
\fIgmtime\fR()
function need not be thread-safe.
.P
The
\fIasctime\fR(),
\fIctime\fR(),
\fIgmtime\fR(),
and
\fIlocaltime\fR()
functions shall return values in one of two static objects: a
broken-down time structure and an array of type
.BR char .
Execution of any of the functions may overwrite the information
returned in either of these objects by any of the other functions.
.P
The
\fIgmtime_r\fR()
function shall convert the time in seconds since the Epoch pointed to by
.IR timer
into a broken-down time expressed as Coordinated Universal Time (UTC).
The broken-down time is stored in the structure referred to by
.IR result .
The
\fIgmtime_r\fR()
function shall also return the address of the same structure.
.SH "RETURN VALUE"
Upon successful completion, the
\fIgmtime\fR()
function shall return a pointer to a
.BR "struct tm" .
If an error is detected,
\fIgmtime\fR()
shall return a null pointer
and set
.IR errno
to indicate the error.
.P
Upon successful completion,
\fIgmtime_r\fR()
shall return the address of the structure pointed to by the argument
.IR result .
If an error is detected,
\fIgmtime_r\fR()
shall return a null pointer and set
.IR errno
to indicate the error.
.SH ERRORS
The
\fIgmtime\fR()
and
\fIgmtime_r\fR()
functions shall fail if:
.TP
.BR EOVERFLOW
The result cannot be represented.
.LP
.IR "The following sections are informative."
.SH EXAMPLES
None.
.SH "APPLICATION USAGE"
The
\fIgmtime_r\fR()
function is thread-safe and returns values in a user-supplied buffer
instead of possibly using a static data area that may be overwritten by
each call.
.SH RATIONALE
None.
.SH "FUTURE DIRECTIONS"
None.
.SH "SEE ALSO"
.IR "\fIasctime\fR\^(\|)",
.IR "\fIclock\fR\^(\|)",
.IR "\fIctime\fR\^(\|)",
.IR "\fIdifftime\fR\^(\|)",
.IR "\fIlocaltime\fR\^(\|)",
.IR "\fImktime\fR\^(\|)",
.IR "\fIstrftime\fR\^(\|)",
.IR "\fIstrptime\fR\^(\|)",
.IR "\fItime\fR\^(\|)",
.IR "\fIutime\fR\^(\|)"
.P
The Base Definitions volume of POSIX.1\(hy2017,
.IR "Section 4.16" ", " "Seconds Since the Epoch",
.IR "\fB<time.h>\fP"
.\"
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
In the event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
.PP
Any typographical or formatting errors that appear
in this page are most likely
to have been introduced during the conversion of the source files to
man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
